Brother Dear
by CJS51703
Summary: Whoever knew that Undyne had a brother? (Rating may change.)
1. Chapter 1

*****Hello, everyone! So, a few things to say: I wasn't originally going to post this. But I talked to a friend and they convinced me to post it. So it's their fault. Also, I was going to post it last night... but I got sick. So here I am! Alphys and Undyne belong to Toby Fox, a certainly character belongs to me, and let's get started!**

 **Chapter One: The Twinless Twin Is Back Again**

He put his fingers in his pockets, feeling a sort of nervous sense hit him. He shook it off, however; this was his _sister_ , apparently.

 _Yeah, the sister you've not spoken to for the entire duration of your life,_ he thought. But, he shook that thought to the side.

Rather, he walked up to what was presumably the right address. And he pounded on the door.

Then, he had to wait.

XxX

Undyne and Alphys were attempting to watch anime together. The fact that Mettaton kept texting and trying to call his maker meant that it was a little hard to enjoy some "girlfriend" time.

When Alphys eventually did answer all of his questions and got to put her phone away, they heard a rough pounding at their door.

"If that's Mettaton, I'm killing him," Undyne grumbled, standing up to get the door.

"M-maybe don't kill h-him," Alphys said as she paused their anime.

Undyne stopped and turned to look at her. "...I'll only thrash him." Then, she went to the door. Rather than finding Mettaton, she found someone else.

Someone who looked _extremely_ similar to her.

The main difference was that this new person was a male. He was a fish monster, yes, with cerulean scales, red hair, and yellow eyes with black slits for pupils. But his hair was far shorter, while still hanging a bit in his eyes. He wore a green t-shirt, black jeans, and red sneakers.

On one of his crossed arms was a tattoo. A series of Roman numerals. A date, judging by the amount. But what that date was, Undyne had no idea. She just stood and stared at her genderbent reflection.

"Ya gonna stare at me or let me in?" The male asked.

Undyne regained her composure. She crossed her arms and leaned slightly against the doorframe. "Y'know, I generally don't let strangers into my house," she said.

The male snorted. "It may come as a surprise, Undyne," he said, putting emphasis on her name, "but I've known you for a while. Known _of_ you, at the least."

Now, Undyne was starting to get frustrated. She stood upright. "You can tell me what's going on right now, or I can carry you off of my porch with a spear," she threatened.

The male held up his hands. "I was trying to be cool about it, but okay. My name's Kamen, I would rather _not_ be impaled..." Kamen began.

He added with a slight smile, "...and I would also happen to be your brother."

 *****Happy now, Smiles? Anyways, be sure to leave a review on the way out and I'll see you all in the next one! Bye!**


	2. Chapter 2

*****Hello, everyone, and Happy New Year! I would have uploaded this yesterday, but it was my brother's birthday and I also had a ton of homework to complete. So this does reference my one-shot On My Own, although Kamen does seem to hit the higher points of it. Anyways, Alphys and Undyne belong to Toby Fox, Kamen belongs to me, and let's roll!**

 **Chapter Two: Seriously?**

Undyne raised an eyebrow, clearly not buying it. "Can ya prove it somehow?" she asked.

"Just ask me only what you think your brother-twin brother, to be exact-would know," Kamen said. So, Undyne did just that.

"When's our birthday?"

"November 19."

"Which one of us is older?"

"I am."

"By how much?"

"Two minutes."

"So close. Anyways, what were our parents' names?"

"Jasper and Onika Undying."

"Would we ever have gotten to meet Dad?"

"No, he died in the war before Mom had us."

Undyne nodded-every answer was correct, or seemed like something only a brother would know. "Fine. Come in," she finally allowed.

"At last," Kamen said. He walked inside. Undyne shut the door and lead him to the living room.

"H-hey, Undy-" Alphys stopped mid-sentence. It's not every day that you think you're seeing two of your girlfriend.

Kamen, however, felt his SOUL skip a beat. He sat down on the arm of the couch where Alphys was. "And what would _your_ name be, beautiful?" he asked.

Alphys blushed madly, feeling about seven different types of awkward just then. Until Kamen was pushed off of the arm of the couch and into the floor.

Undyne sat down next to Alphys, a protective arm going around her shoulder. "This is Alphys. And she's _my_ girlfriend, punk!" she snapped.

Kamen stood up and looked a little disappointed. Then, he actually thought of something else. "Huh. I didn't know that you were a lesbian," he commented.

"If you have a problem with that, I'm kicking your butt and then kicking you out," Undyne said simply.

"C-can you please t-tell me who you a-are?" Alphys asked.

"Kamen. Undyne's older brother," Kamen replied. "Twin brother that I didn't know I had until about five minutes ago," Undyne added on.

Alphys' eyes widened behind her glasses. "...oh my God," she said simply.

"That's about how I feel about it. However... Kamen here says that he's known about me his whole life," Undyne said. "Then wh-why didn't you c-come to her sooner?" Alphys asked.

"Well, gorgeo-" Kamen caught Undyne's look just then. "Anyways, that circles back to a long story that ultimately leads up to right now."

"We both have time," Undyne shrugged. Alphys nodded to agreed. So, they turned to look at Kamen, who sat on the couch next to them.

"Well, we call it a story of separation at birth, it seems like. The only baby Mom took home from the hospital was Undyne. I was left. An orphanage-or a sorry, sorry excuse for one-kept me until I was about... eight or nine years old. Then, I was moved to foster care. And I was passed from home to home to home. Some abusive, some caring, some about so-so. Only half of 'em even learned my name. When I was eighteen, I took up residence anywhere I could get. Never had a permanent home. But I did learn, however, that I wasn't alone. Because I began poking around family records in the Snowdin Librarby when I slept in there one night. And lo and behold, what did I find? My family. Deceased mother, deceased father, my living self, and a living sister. One living, successful Undyne Amali Undying. I had to do some digging after we got to the surface. But I found ya! With a nice house and a beautiful girlfriend. And I've. Got. Nothing," Kamen explained. He looked at Undyne. "And what did you do?" he asked coldly.

"Lived with Mom for seven years, was homeless until I was nine. I got adopted, then joined the Royal Guard at eighteen. I worked my way up to the Captain and I held the spot until we got to the surface. I got a job as a cop and moved in with Alphys," Undyne explained.

Kamen looked at his sister's girlfriend. "And there ya have it. The stories of the Undying siblings," he said.

Alphys nodded. Then, she noticed something. "Wh-what's your tattoo?" she asked.

Kamen looked at his arm. "Don't bother with it," he said flatly. So, Alphys decided to agree to that. For now.

"Well, other than hitting on taken girls," Undyne said, "what else do you do?" Kamen looked at her. Then, he stood up and summoned twin katanas. "These come in handy," he said.

Undyne whistled, impressed. "Do you wanna go?" she asked. She held out her own spear.

"Please, n-not in the h-house," Alphys sighed.

"Oh, yeah. She, ah, has a ban on weapons in the house. Even for cooking, which is another thing I use weapons for," Undyne said.

"Then we'll take it outside," Kamen said, grinning.

Brother and sister put away their weapons for the moment and went on outside.

Two things were on Alphys' mind. The first was that feeling that she didn't or couldn't quite trust Kamen. The second was the surprise that Undyne's middle name was Amali.

 *****The date November 19 and name Amali were just kinda taken out of nowhere. Anyways, be sure to leave a review on the way out and I'll see you all in the next one! Bye!**


	3. Chapter 3

*****Hello, everyone! *blows dust off of story* Sorry it took so long for an update... I got sidetracked. But today is a day off for me—hooray exam exemption policy—so I have a chapter. It ain't the best, but this story is hard to get something really good for. Alphys and Undyne belong to Toby Fox, Kamen belongs to me, and let's roll!**

 **Chapter Three: Lacking In Trust**

Kamen wound up being allowed to stay in the guest room that night. As it turned out, he was looked for a place to stay.

So, Undyne had agreed to let him stay under the condition that he made no more advances on Alphys. He had agreed, but only for the reason that he would rather sleep in a house than a car. Plus, he had deducted that Undyne and him were at about the same level when it came to fighting skills.

One step out of line, and she could easily turn the tables to kick his butt.

XxX

That night came. Undyne and Alphys were in their room.

"C-can I be h-honest about s-something?" Alphys asked.

"Yeah, but it's a first to hear you say that," Undyne said.

Alphys decided to ignore that comment. "I d-don't really... t-trust your brother," she admitted.

Undyne sighed and sat down with her girlfriend. "Listen, Alph. I know you have issues trusting in new people. And I'd be lying if I said I completely trusted Kamen right now. But... he's still my brother, and you might wanna get used to him before—" She stopped mid-sentence.

Alphys was confused, if not somewhat concerned. "B-before what?" she asked.

Undyne thought about it, then shook her head. "Forget I said anything about that last part. My point is, he's still my only family member, so can you please at least make an effort to try and hit a mutual level with him? I'll talk to him about this too. I don't ask much of you," she said.

Alphys thought about it for several moments. "...f-fine," she finally agreed.

As they both went to sleep, there was something that neither of the girls were aware of.

It was that Kamen had heard every word.

And he was _not_ happy about it.

 *****Well, it's short too. Anyways, be sure to leave a review on the way out and I'll see you all in the next one, which will hopefully be longer and somewhat better.**


	4. Chapter 4

*****Hello, everyone! Normally, I have an outline written for each chapter. This one just kinda... came as it came, but I think it came out well. Kamen belongs to me, Undyne and Alphys belong to Toby Fox, and let's roll!**

 **Chapter Four: Listen Here**

Kamen went off to his room. However, he didn't sleep. He shut the door and sat down on the bed. He looked at his tattoo and sighed. Forever on his arm was the day he'd been to his own mother. His birthday.

Undyne's birthday as well.

He'd gotten it done as a promise. As a promise to himself and a reminder. A reminder that he would find his sister. No matter how many years he took, no matter how many places he had to look, he would find Undyne. And now, he'd done so.

But he'd also found someone else. And he _didn't_ like her.

Now, he knew that he wasn't the most trustworthy person. He had certainly learned that. But he knew that there was no way in hell that he could get close to Undyne with Alphys in the picture. At least, not as close as he wanted to be. He'd been searching for _years_ to find Undyne. Now that he'd found her, he wasn't gonna let some... some _fat little dinosaur nerd_ get in the way.

And he was going to fix that

XxX

Undyne wasn't home from work yet. Alphys had just gotten home from work herself. When she got to the living room, she saw Kamen sitting there, his magic katana leaning against the chair he was sitting in.

"Hey, Alphys. Did you have a good day at work?" he asked, looking at and fiddling with his weapon of choice. His tone was mocking friendliness, and was a lot like that of a shark circling in a tank.

And Alphys was right over it.

She tried to keep her nerves calmed. "Y-yeah," she forced out.

Kamen stood up and walked over, his katana over his shoulder. "Listen, shorty. I thought were hot at first-I won't lie. But Undyne really... really... _really_ loves you. And for me, her _twin brother_ , her siblings who she hadn't met and didn't even know existed until yesterday, that's not good. She talks about you a lot," he began.

Alphys bit her lip nervously, taking a few paces back, her tail twitching. "I-I mean, it's a b-bit inevitable. Sh-she's my g-g-girlfriend," she reasoned. The flat part of a katana was then forced against her neck.

"Listen. My point is short and simple. I want you to screw off from my sister. You? You're nothing. One girlfriend. She'll be over you in no time. Me? I'm her brother. You're a big scientist, and you can tell that biological relations are the strongest. Easy. So run along. I don't care where to. Just go. If you don't, then... well... I may not be so nice with my katana. We clear?" Kamen asked.

Alphys tried to control her shaking, gritting her teeth nervously. She was trying to sort out the thoughts and responses and emotions that were all clambering for space in her mind. She was suddenly much more aware that a deadly weapons was at her neck, ready to dust her with one turn of a wrist. She swallowed her fear and nerves and sighed. She let one word escape her lips.

"Y-yes."

Kamen smiled. He dispelled his katana. "Good. Glad we see eye to eye on this. So get outta here," he snapped.

"C-can I at least g-get my th-things? I live h-here," Alphys said.

Kamen thought about it. Then, he nodded. "Sure. Go ahead," he allowed.

Alphys got right out of there. She wasn't going to leave-no, that wasn't happening.

But Undyne had to know what was going on.

 *****And... I'm gonna have to leave you there. I hope you all enjoyed and I'll see you all in the next one! Bye!**


	5. Chapter 5

*****Hello, everyone! So, for those of you who aren't aware, I do have a headcanon that Undyne occasionally smokes. It's not really a spoiler, but I'm just saying that because I don't want anyone barking at me like my dog at 2 AM in the reviews. Anyways, Alphys and Undyne belong to Toby Fox, Kamen belongs to me, and let's roll!**

 **Chapter Five: Over Smoke**

When Undyne came home, she saw Kamen out in front of her house. So, she got out of her car and went over to him.

As it turned out, he was smoking. "Hey," he said.

"Hey," Undyne replied.

Kamen fished a cigarette out of his pack and held it out. "Want one?" he offered.

"Nah. I only smoke after really bad days. 'Sides, it's not my brand, and I should probably let Alphys know that I'm home," Undyne said.

"Speaking of Alphys... she told me something today. She told me that she was gonna leave you," Kamen said.

Undyne's eye widened. "Wha-why? What did I do?" she asked.

Kamen shrugged. "I don't know. She didn't say. But she's probably inside, packing up her things," he said.

Undyne frowned, ear fins drooping. What had she done wrong? She'd done her best to make Alphys happy, even if she was a bit aggressive. At last, she looked at Kamen. "Gimme a cigarette," she said. She took it and lit it, putting it in her mouth.

They both leaned against the wall outside, both chainsmoking silently. They passed the cigarette box and lighter between each other. Eventually, they did run out.

"Want me to get more?" Kamen asked.

"No. I have some in my nightstand. And I gotta ask Alphys about this before she runs off," Undyne said. Before she could go inside, Kamen grabbed the back of her shirt.

"What?" she asked, turning to him.

"Just remember," Kamen said, smiling slyly, "you're still being left."

Undyne pried her shirt from his grasp. "I know," she said.

Then, she walked away.

XxX

When Undyne went inside, she ran right into Alphys. They both stared at each other for at least a minute, bespectacled eyes meeting one eye.

"...h-have you been s-smoking again?" Alphys asked.

"Yeah. Because Kamen told me that you're leaving me. If you're gonna leave, then you can at least tell me why. Because I can fix it," Undyne said.

Alphys was the one to be surprised now. "Wh-what the... I-I'm not leaving! K-Kamen threatened m-my life if I d-didn't get out. I don't w-want to leave you, b-because I love y-you," she said.

Undyne sat on her knees and was just about to give her girlfriend a kiss. Until she was interrupted.

"You're a good liar, I'll give you that much."

The voice belonged to Kamen, who'd come in with Undyne. She looked at him. "Why did you threaten her? What did she do to you?" she barked, standing back up.

"She's a good liar. She told me that she was leaving you," Kamen shrugged. Undyne looked back at Alphys.

"H-he really th-th-threatened me!" she insisted.

"Sis, it's me or her. Something that's temporary, or your only remaining family member," Kamen said.

He had a point. He was sketchy, but he was family. Alphys loved Undyne, but she still had a tendency to lie after all these years. Undyne looked between them both.

"I-I..."

 *****Okay, this is somewhat off-topic, but in my chorus class, we're working on a song arranged by someone with the name Undyne. I couldn't make this up if I tried. Anyways, be sure to leave a review on the way out and I'll see you all in the next one! Bye!**


	6. Chapter 6

*****Hello, everyone! Here we are, last chapter. And I'm pretty happy with how it came out. Not all of my projects can be a bazillion and three chapters long, you know. Anyways, Alphys and Undyne belong to Toby Fox, Kamen belongs to me, and let's roll!**

 **Chapter Six: If You'll Sit Down and Shut Up (Final)**

Following Undyne's stammered response came two different replies.

"Do ya really think I'd lie to you?" Kamen asked.

Alphys glared lasers at him-well, she tried. "Y-you did just n-now!" she point out.

"Two of a kind. So did you," Kamen said.

Then, they started talking at the same time. Talking then became yelling. Yelling then included pushing.

"SHUT UP, _BOTH_ OF YOU!"

Undyne's shouting silenced both of them. Kamen and Alphys both looked at her at once, not looking at each other.

"I'm not gonna stand here and listen to you yelling and fighting like a bunch of bratty kids. You aren't even using weapons. But, I have a way to settle this. Both of you, sit down, shut up, and don't try to kill each other. I'm not gonna pry you apart. I'm not your mom. Now, I'll be back in a second," Undyne said. Then, she left.

Kamen and Alphys both plunked down on the couch. They were sure to sit down on opposite sides, not looking at each other. The silence made Alphys squirm, and it made Kamen just want to slap her senseless and get it overwith.

Before either of those things could happen, Undyne came back. But there was nothing different about her. At least, there wasn't anything different on the surface.

"Hey, Kamen," she said, crossing her arms and shifting her weight to one side, "I've been meaning to ask you this, but what does that tattoo mean?"

Kamen glanced at the Roman numerals that were forever on his forearm. "Your birthday. Our birthday. I got it done as a reminder... a reminder that I _had_ to find you, and you only. Not with anyone else. I say that I'm your only family. But you gotta remember... that makes you my only family. I've been alone, and I need my baby sister. That's why I got a tattoo of our birthday. A reminder, and a promise. A promise that I'd find you, that I made to myself," he explained. His tone was getting thick at the last part, but he coughed and cleared it up.

Undyne met her eye against both of his. Then, she nodded. "Got it," she said quietly.

Then, she turned her attention to Alphys. "Answer me this. Are you gonna leave me?" she said.

"N-no, I would n-never. I l-love you," Alphys said.

"Then we'll prove it with what you say next. I was gonna ask you in a better setting, but... we gotta settle this, or I'll never get peace," Undyne said. She reached into her back pocket and pulled out a small ring. "It's what I went upstairs for. I've kept it in my nightstand for weeks now, trying to figure out how to ask. Kamen, I keep my cigarettes in my nightstand too. That's the... real reason I didn't want you to go get more," she admitted.

She knelt down in front of Alphys, a slight smile on her face. "It's a formality to ask by now, but... will you marry me?" she asked.

Alphys' hand went over her mouth, but she was evidently smiling. "Y-yes. Yes, yes, y-yes," she said once she moved her hand away from her mouth.

Undyne slid the ring onto her left ring finger, then stood up and kissed her softly.

"And please, tell me what a marriage proposal has to do in the slightest with settling this?" Kamen asked, bored.

Undyne's smile because a smirk as she stated the final part of her little plan to get a truth here.

"If Alphys was really leaving me, I don't think she would've agreed to spend the rest of her life with me just now."

Kamen then realized that. His mouth opened and closed several times-his lie was too imperfect to last. He finally sighed, his ear fins drooping. "Ya got me," he admitted, sounding defeated.

"So ya threatened her life and lied to me about it," Undyne said, anger in her tone.

"It's just like I told you! I wanted to find you, and you alone. I had to run her off somehow. And if a death threat did the trick, then so be it," Kamen said.

"That is, by far, the most screwed-up logic I've ever heard. And my best friend is Papyrus," Undyne stated.

Kamen sighed and stood up. "And this is the part where you want me to leave and-slash-or want to disown me. Well, fine. I'm used to it," he said. Before he could walk off too far, he was pulled backwards by the back of his shirt.

"And who said that I wanted you to leave?" Undyne asked.

That shocked both Kamen and Alphys, who was still watching this unfold.

"Huh?" Kamen asked, that being the only thing he could get out currently. The grip on his shirt was released.

"Listen. You did lie to me on something important, and I am going to kick your butt later for that. That's a fact of life. But, like you said, we're what's left of our family. You may get on my nerves every now of then... but isn't that what a brother does? Annoys his sister?" Undyne asked.

Kamen grinned and clapped her on the back. "Yep. But I'm guessing you want me to move out?" he asked, a little sad about that part.

"You can stay here until you get a place of your own," Undyne allowed.

Kamen fist-pumped.

"But don't look so victorious yet. You threatened Alphys' life. Therefore, I'm obligated to do this," Undyne said. And she punched Kamen so hard that he fell to the floor.

Alphys stood up and looked at him, then to Undyne. "I-I don't really think th-that was n-n-necessary," she said. Undyne took her hand.

"Yes it was, Alphys," she said. "Yes, it was."

 **The End**

 *****And, there you have it. The ending of this story, take it or leave it. (That was sarcasm.) Be sure to leave a review on the way out and I'll see you all in the next one! Bye!**


End file.
